The truth is, yes casinos can control a slot machine or rig it only to give players small wins. Some casinos work with developers to create exclusive games. This gives them even more access to a game's code and RNG.
Predicting a slot machine's payout is not possible, as modern slot machines use random number generators to determine the outcome of each spin. These random number generators ensure that each spin is independent of the previous one, making it impossible to predict the outcome with certainty.